The present invention relates to a scintillation material with defined oxygen content and to a process for the production thereof. In particular, the scintillation material of the present invention is characterized by its manufacturing process, so that the following description also refers to this process, although the invention is a material as such.
The scintillation material according to the invention has advantageous properties. In particular, the detection properties of the scintillation material produced according to the invention are improved.
Moreover, particular embodiments of the invention also exhibit an advantageous strain birefringence (SBR) and a high homogeneity of the refractive index (HOM).
The process according to the invention also makes it possible to produce a scintillation material, which in addition to the aforementioned positive properties also exhibits particularly great mechanical ruggedness. Namely, special processes according to the invention make it possible to use suitable dopants in the scintillation material. Such materials represent particularly special embodiments of the invention.
Prior art halide-based scintillation materials have the disadvantage that during their production water and oxygen stemming either from the processed raw materials or from the environment form oxyhalides in the melt, which cause strains in the material during the crystallization. These undesirable strains are due to precipitates that form during the crystallization process and that exert a considerable negative influence on the mechanical properties of the material. In particular, the prior art scintillation materials have a tendency to fracture. Moreover, a decisive parameter of the material, namely the light yield or light output, is reduced.
Furthermore, the known manufacturing processes lead to low yields.
Prior art scintillation materials or scintillation materials produced in the usual manner also have poor workability, which is due to their increased fracture tendency. Fracture tendency can be due to inhomogeneities in the material caused by thermal strains and also by crystal defects. The presence of thermal strains can bring about a pronounced strain birefringence of the scintillation material and also refractive index inhomogeneities. In some cases scintillation materials produced in the usual manner even exhibit considerable differences in terms of light yield, mechanical properties and behavior following after-treatment. This is particularly evident in the case of single crystal materials which show crystal-to-crystal differences in behavior. An excessive amount of oxygen in the material has a negative effect on essential properties.
After-treatment of the materials produced in the usual manner, such as separation, grinding and polishing, requires a considerable effort leading to considerable numbers of rejects which in the past have been referred to as being disadvantageous.
Major crystal-to-crystal differences in terms of scintillation properties are also viewed as being disadvantageous.
The materials and processes according to the present invention are not limited to single crystal scintillation materials and their production, although these represent special embodiments. According to the invention, it is also possible to produce and provide polycrystalline materials. Such polycrystalline structures are preferably essentially devoid of interspaces/grain boundaries, which lead to single-crystal-like properties.
Processes for producing single-crystal scintillation materials are preferred, because the processes according to the invention are capable of providing single crystals of a preferred size. When the material is polycrystalline, the individual crystals should be arranged so as to impart an isotropic behavior to the material involved.
Scintillation materials based on cerium bromide are known from the prior art, for example see U.S. Pat. No. 7,405,404 B1. The cerium bromide discussed therein can also be doped. In particular, yttrium, hafnium, zirconium, palladium and bismuth are not mentioned as dopants. Moreover, the processes for producing the single crystal scintillation materials are current processes known to those skilled in the art. Special conditions concerning the atmosphere during crystal-growing are not mentioned. The same is true for cooling conditions or cooling rates used during the manufacturing process.
EP 1 930 395 A2 describes scintillator compositions prepared from different “pre-scintillator compositions”. Nothing is said about the atmosphere present during crystal growing. Annealing regimes and cooling rates are also not mentioned.
US 2008/0067391 A1 discloses, among other things, single-crystal scintillators of a certain formula. It mentions dopants in the materials and does not refer to a particular manufacturing process that would result in a material with reduced oxygen content.